Semiconductor-based optoelectronic devices are used in optical communication systems and other systems.
Various materials have been used to fabricate optoelectronic light emitting devices. In one example, group III and group V elements are combined in various compositions to form layers. One of the material systems that use group III and group V elements is referred to as the gallium nitride (GaN) material system. Typically, layers of group III-V elements are formed to fabricate a semiconductor optoelectronic device. These devices typically include a region referred to as a p-n junction. One or more p-n junctions may form part of a semiconductor optoelectronic device.
For optoelectronic devices formed using the GaN material system, the contact resistance of the p-type material is typically relatively high compared to the contact resistance of the n-type material. Further, the mobility of holes in the p-type material is typically lower than the mobility of electrons in the n-type material. This results in a high series resistance on the p side of a GaN device. A high series resistance elevates the operating voltage of the device and causes the generation of heat, which typically degrades the performance of the device.
One way to minimize the series resistance on the p-side of an optoelectronic device is to incorporate a tunnel junction into the device. When reverse biased, a tunnel junction promotes the flow of electrons from the p-type material to the n-type material, enabling contact to be made to n-type material, thus minimizing contact resistance. In such a device, the amount of p-type material can be minimized, thus minimizing series resistance, and lowering the operating voltage of the device. To achieve maximum benefit from a tunnel junction, the voltage drop across the tunnel junction is typically minimized.